These integrated-circuit power switches join Micrel's MIC2505 and MIC2506 High Side Switches to deliver a broad portfolio of USB devices. Most important, they work with self-powered and bus-powered hub applications to provide exceptional design flexibility.

The USB industry standard is designed to make interconnecting PCs and peripherals more like consumer appliances in terms of ease of use. Users do not have to worry about installing software drivers or add-in boards, for example. "Plug-and-play" USB peripherals will automatically configure themselves and be ready for use immediately. USB provides a serial bidirectional 12-Mbps interface. "Hubs" distribute both serial data and power to all USB devices via a standard four-wire cable.

For self-powered hub applications, Micrel announces the new MIC2525 and MIC2526 USB high-side protected power switches, which are high-performance replacements for passive polyfuse parts. Optimized for USB power distribution, these single and dual high-side switches available with either active-high or active-low logic-level enable are respectively for maximum design flexibility in interfacing to any USB controller.

To meet the requirements for USB power distribution, the MIC2525 and MIC2526 are designed to solve all the issues concerning USB power distribution. For example, they feature an integrated 100-milliohm switch that meets USB requirements for voltage drop and regulation.

These devices will automatically limit current to safe levels, 750mA typically, well under the USB ceiling of 5A. Upon detecting a current-limit condition, the MIC2525 and MIC2526 activate a logic-compatible flag output to the local USB controller for action by the host software. In addition, an undervoltage lockout (UVLO) circuit ensures that the switch will not turn on until the supply voltage is stable.

These devices are fully protected against shorts or other fault conditions by a thermal shutdown circuit that monitors the IC's temperature. When the specified temperature limit is exceeded, the switch is turned off to prevent damage.

The MIC2525 and MIC2526 also feature a soft-start circuit for slow and controlled turn-on. This feature limits the in-rush current that occurs when charging the bulk capacitance of the devices attached to a downstream port. Limiting the current ensures that downstream devices meet the USB transient-drop specification for the bus voltage. These devices may also be used in the peripherals themselves to ensure that the in-rush current is limited.

For USB microcontroller users, Micrel provides the MIC5203 and MIC5207 miniature low-power voltage regulators. These regulators will supply 3.3V to protect lower-voltage microcontrollers from USB's higher bus voltage. These regulators are ideal when the USB controller is powered directly from the bus to support enumeration when the device itself is powered down.

The MIC2525 and MIC2526 also bring the high-spec performance to bus-powered hubs.

Orders can be placed now for the MIC2525 USB-protected FET switch, priced at $0.95 each (1,000-piece quantities), available now. The MIC2526 dual-port version is $1.38 each (1,000 units), available now.